This invention relates to a fluid friction clutch having a primary disk fastened to a live shaft and an output clutch housing, which surrounds the primary disk, having a working chamber which is formed between the primary disk and the clutch housing and into which a shearing fluid can enter from a storage chamber as a function of the position of a valve plate having an armature. The valve plate opens and closes a connection opening between the storage chamber and the working chamber and can be adjusted against a spring effect into an opened or a closed position by a magnetic force caused by a stationary electromagnet coil arranged on the driven side of the shaft.
A liquid friction clutch of this type is known from German Patent Document DE 27 18 723 A1. In this type of construction, the magnetic flux from the electromagnet coil arranged on a stationarily held sleeve is transmitted exclusively by way of the live shaft to the armature of a valve plate arranged coaxially with respect to the shaft. Since the distance between the magnetic coil and the armature to be activated by its field is very large, the coil must have correspondingly large dimensions if a use is to be permitted at all in practice.
One object of this invention is to provide an improved arrangement for a fluid friction clutch which is electromagnetically controlled from the output side. The space requirement of this fluid friction clutch is low and its efficiency is clearly improved in comparison to the known construction.
In order to achieve this object, according to the invention, a fluid friction clutch of the initially mentioned type has the primary disk, or at least a hub of this disk, placed upon the shaft, constructed as a magnetic insulator and provided with a magnetic flux guiding ring. The flux guiding ring extends into the proximity of the armature of the valve plate and rests against the bearing for the clutch housing which is placed on the hub and is in a magnetic shunt with the electromagnet coil.
This development achieves a very effective magnetic field construction which, in turn, results in an electromagnet coil which will not become too large. This new fluid friction clutch is advantageous in that it can be controlled from the live side, that is, as a rule, from the engine side, and is extremely compact.
As a further development of the invention, a second flux guiding ring may be arranged concentrically within the first flux guiding ring and on an end of the shaft facing the valve plate. The second flux guiding ring also ends just in front of the armature of the valve plate. The magnetic field can thus be connected by way of the core area of the shaft.
As yet a further development of the invention, the two sleeve-shaped flux guiding rings can form the inner boundary of the storage chamber which is fixedly connected with the primary disk and is bounded to the outside by axially projecting ring ribs of the primary disk. In this construction, as a further development of the invention, axial boundaries of the storage chamber can be provided by the primary disk, on the one side, and by a separating wall, on the other side, which is fixedly inserted into the ring ribs and has a decentrally arranged connection opening which can be closed by the valve plate.
As a further development of the invention, this connection opening can be covered by a guiding plate on the side facing away from the storage chamber. The guiding plate guides the emerging shearing fluid directly into the outer area of the working chamber. As the result of this measure, the emerging shearing fluid can be supplied directly to the outer area of the working chamber which, as a rule, is constructed as a profile area. Depositing of shearing fluid on the interior side of the clutch housing, which also slowly rotates, is avoided.
As a further development of the invention, the storage chamber may also be divided into two concentrically arranged "areas" or volumes by the arrangement of two concentrically extending ring ribs which project axially from the primary disk. The area radially inside the interior ring rib is covered by another separation disk toward the second outer ring surface, which separation disk is provided with at least one flow-through bore. As a result of this measure, overfilling of the working chamber is avoided at low driving speeds. A shorter disconnecting time of the clutch can therefore be achieved at these low rotational or driving speeds. With a corresponding arrangement of the flow-through bore, at higher driving speeds, more and more shearing fluid from the inner part of the storage chamber will flow by way of the flow-through bore into the outer storage chamber. This fluid can flow from the outer storage chamber through the connection opening into the working chamber.
In yet another development of the invention, the sleeve-shaped flux guiding rings assigned to the armature of the valve plate also form a portion of the storage chamber and are therefore provided with radial overflow openings which open into the adjacent portions of the storage chamber. As a further development of the invention, in this embodiment, the return flow of the shearing fluid from the working chamber may take place in a known manner by way of pumping bodies and through a return flow opening which is arranged in a separating wall fixed to the clutch housing. This return flow opening advantageously is centrally arranged in the separating wall and is provided with a sleeve which leads into the central area of the storage chamber which is bounded by the inner sleeve-shaped flux guiding ring.
As an even further development of the invention, the valve plate may be arranged on the separating wall so as to swivel and may be swivellable about a spring joint which, when the magnetic coil is currentless, holds the valve plate in the opened position of the connection opening. As a result, the fluid friction clutch becomes fail-safe.
Finally, as a further development of the invention, it is possible to construct the outer sleeve-shaped flux guiding ring for the armature as a part which is integrally cast with the primary disk. The magnetic coil may adjoin the clutch housing as closely as possible and may be provided with flux guiding rings with radial gaps to the shaft. In this case, one of these flux guiding rings adjoining the magnetic coil may be fixedly pressed onto the shaft. A second flux guiding ring on the magnetic coil may be fixedly connected with it and, on its interior side, may form a very small radial gap with the shaft.